Elastic shaft joint and elastic bush forming method

ABSTRACT

An elastic shaft joint is constituted of a joint member, a shaft member being fitted in a shaft of the joint member, and an elastic bush having a cylindrical inner sleeve fitted and fixed on the joint member, a cylindrical elastic member fixed on an outside surface of the inner sleeve, and a cylindrical outer sleeve fixed on an outside surface of the elastic member, for elastic torque transmission between the joint member and the shaft member, wherein the outer sleeve is fixed on the shaft member.

[0001] This application claims the benefit of Japanese Patent Applications No. 2001-146803 and No. 2001-285516 which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an elastic shaft joint used for a steering apparatus of an automobile and a method of forming an elastic bush thereof, and particularly to technique for effectively absorbing displacement in the axial direction while securing comparatively high torsional rigidity.

[0004] 2. Related Background Art

[0005] A steering apparatus of an automobile and the like is constituted of a steering wheel for a driver's steering, a steering gear for shifting the direction of dirigible wheels and a steering shaft for connecting the steering wheel and the steering gear. In such a steering apparatus, since the steering gear is scarcely located on the axial center line of the steering wheel, there are used a plurality of steering shafts connected by a universal joint. Such a universal joint for steering shafts is generally a Cardan joint in which a cross piece (joint cross) is movably mounted between a pair of joint elements, as disclosed in the U.S. Pat. No. 3,501,928.

[0006] Recently, an elastic shaft joint with an elastic member of synthetic rubber or the like has been proposed in order to reduce transmission of kickback from the road surface to the steering wheel. In this type of elastic shaft joint, one joint element of a Cardan joint is separated into a joint member (yoke) and a shaft member (shaft), and an elastic ring of synthetic rubber, etc. is mounted between the yoke and the shaft. In order to prevent damage to the elastic ring and to enhance durability thereof, the yoke and the shaft are provided with stopper portions to limit more than the predetermined amount of relative rotation.

[0007] For example, the Japanese Patent Application Laid-Open No. 6-329033 and the Japanese Patent Application No. 11-324100 disclose an elastic shaft joint (first conventional device) wherein a comparatively shorter elastic bush is mounted between a yoke and a shaft. Also, the Japanese Patent Application Laid-Open No. 9-229086 discloses an elastic shaft joint (second conventional device) wherein a pair of flat plate type elastic members is mounted between a yoke and a shaft. Further, the Japanese Utility Model Application Laid-Open No. 4-69283 and the Japanese Patent Application Laid-Open No. 8-200382 disclose an elastic shaft joint (third conventional device) wherein a comparatively longer elastic bush is mounted between a yoke and a shaft. Also, the Japanese Utility Model Examined Publication No. 59-29147 and the Japanese Patent Application Laid-Open No. 60-159418 disclose an elastic shaft joint (fourth conventional device) wherein two sets of elastic bushes are mounted separately away from each other between a cylindrical yoke and a cylindrical shaft. Furthermore, the Japanese Patent Application Laid-Open No. 10-19054 discloses an elastic shaft joint (fifth conventional device) wherein an elastic member is disposed slidably in the axial direction in a corrugated cylindrical outer sleeve fitted on a yoke, and the outer sleeve is fixed to a shaft.

[0008] However, the above-mentioned elastic shaft joints have various properties and malfunctions caused by the properties. In the first conventional device, since other than the only one shorter elastic bush is not utilized, even though comparatively small force acts on the yoke and the shaft, the angle between the yoke and the shaft is easily changed, i.e., the yoke and the shaft are easily inclined to each other. Also, in the second conventional device, since the elastic members are not disposed circumferentially, the yoke and the shaft are easily inclined to each other in predetermined directions similarly to the first conventional device. Further, in the third conventional device, the longer elastic bush is utilized, so that the torsional rigidity can be kept comparatively high, but displacement of the yoke and the shaft becomes difficult in the axial direction. Further, in the fourth conventional device, the diameter of the elastic bushes is reduced. Therefore, when the strength of the elastic members is raised to secure the torsional rigidity, displacement of the yoke and the shaft becomes difficult in the axial direction. Furthermore, in the fifth conventional device, in order to slide the outer sleeve and the elastic member smoothly without looseness, high accuracy is required to form the outer sleeve and the elastic member. In addition, the yoke and the shaft are easily inclined similarly to the first and second conventional devices.

[0009] In the first, second and fifth conventional devices, due to easy inclination of the elastic shaft joint, when a driver turns a steering wheel from right to left, torque is hard to be transmitted to a steering gear, resulting in bad response of the steering system lacking in feeling of rigidity. In addition, excessive inclination of the elastic shaft joint causes large tensile and compressive deformation of the elastic member, leading to shortening of the lifetime of the device. Furthermore, in the third conventional device, preferable results can be obtained in respect to torsional rigidity and nonoccurrence of easy inclination. However, due to the difficult displacement in the axial direction, vibration from the steering gear is transmitted to the steering wheel and noise tends to be generated.

[0010] On the other hand, in the fifth conventional device, as the two sets of elastic bushes are provided away from each other in the axial direction, the inclination of the yoke and the shaft can be nearly neglected. However, the elastic bushes are disposed in the cylindrical yoke, so that when the diameter of the elastic bushes is increased, the weight of the device increases largely. On the other hand, when the diameter of the elastic bushes is kept small and a material with high strength is used for the elastic members, stability of response in steering is improved, but displacement in the axial direction is difficult similarly to the third conventional device.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide an elastic shaft joint and an elastic bush forming method realizing effective absorption of displacement in the axial direction while securing comparatively high torsional rigidity.

[0012] In order to achieve the above objects, according to a first aspect of the present invention, an elastic shaft joint is constituted of a joint member; a shaft member being fitted in a shaft of the joint member; and an elastic bush having a cylindrical inner sleeve fitted and fixed on the joint member, a cylindrical elastic member fixed on an outside surface of the inner sleeve, and a cylindrical outer sleeve fixed on an outside surface of the elastic member, for elastic torque transmission between the joint member and the shaft member, wherein the outer sleeve is fixed on the shaft member.

[0013] In the first aspect of this invention, since the elastic bush is disposed on the outside surface side of the joint member, the diameter of the elastic member of the elastic bush becomes comparatively large, by which torsional rigidity of the elastic shaft joint is improved naturally.

[0014] According to a second aspect of the present invention, an elastic shaft member is constituted of a joint member; a shaft member being fitted in a shaft of the joint member; an elastic bush having a cylindrical inner sleeve fitted and fixed on the joint member, an elastic member fixed on an outside surface of the inner sleeve, and a cylindrical outer sleeve fixed on an outside surface of the elastic member, for elastic torque transmission between the joint member and the shaft member; and a torque transmitting member whose one end is fitted and fixed on the elastic bush and whose other end is fixed on the shaft member, wherein the elastic member is lopsidedly distributed largely on both end sides in the axial direction between the inner sleeve and the outer sleeve.

[0015] According to the second aspect of the present invention, since the elastic member is lopsidedly distributed largely on both end sides of the elastic bush in the axial direction, it is possible to reduce rigidity of the elastic shaft in the axial direction while making it hard to be inclined.

[0016] According to a third aspect of the present invention, an elastic shaft joint is constituted of a joint member; a shaft member being fitted in a shaft of the joint member; a plurality of elastic bushes each having a cylindrical inner sleeve fitted and fixed on the joint member, an elastic member fixed on an outside surface of the inner sleeve, and a cylindrical outer sleeve fixed on an outside surface of the elastic member, for elastic torque transmission between the joint member and the shaft member; and a torque transmitting member whose one end is fitted and fixed on the plurality of elastic bushes and whose other end is fixed on the shaft member, wherein the plurality of elastic bushes are disposed between the joint member and the torque transmitting member on both end sides in the axial direction.

[0017] In the third aspect of the present invention, since the plurality of the elastic members are disposed on both end sides of the torque transmitting member in the axial direction, it is possible to reduce rigidity of the elastic shaft joint in the axial direction while making it hard to be inclined.

[0018] Preferably, in the elastic shaft joint of the third aspect of the present invention, the plurality of elastic bushes constitute plural sets each which has the elastic member with different rigidity, and the elastic members with high rigidity are disposed on both end sides in the axial direction between the joint member and the torque transmitting member.

[0019] In this case, since the rigidity of the elastic members are gradually increased toward both end sides in the axial direction, it is possible to reduce rigidity in the axial direction further with respect to the elastic shaft joint in the third aspect.

[0020] Preferably, in the elastic shaft joint in the first aspect of the present invention, after the inner sleeve, the elastic member and the outer sleeve are fixed to form the elastic bush, in order to subject the elastic member to compressive deformation, the diameter of the inner sleeve is increased or the diameter of the outer sleeve is decreased.

[0021] Thereby, since the elastic member is compressed beforehand, the fixing strength between the elastic member and both the sleeves is improved and also durability of the elastic member at the time of relative displacement of the inner sleeve and the outer sleeve in the rotational or axial direction is improved.

[0022] In the elastic shaft joint of the second or third aspect of the present invention, after the inner sleeve, the elastic member and the outer sleeve are fixed to form each elastic bush, in order to subject the elastic member to compressive deformation, the diameter of the inner sleeve is increased or the diameter of the outer sleeve is decreased.

[0023] Thereby, since the elastic member is compressed beforehand, the fixing strength between the elastic member and both the sleeves is improved and also durability of the elastic member at the time of relative displacement of the inner sleeve and the outer sleeve in the rotational or axial direction is improved.

[0024] In the elastic shaft joint of the second or third aspect of the present invention, a cross section of each elastic bush taken perpendicular to the axis of the elastic bush is formed noncircular so as to subject the elastic member to compressive deformation at the time of relative rotation of the inner sleeve and the outer sleeve.

[0025] Accordingly, at the time of relative rotation of the inner sleeve and the outer sleeve, the elastic member is subjected to compressive deformation, so that it is possible to improve torsional rigidity without increasing rigidity in the axial direction in vain.

[0026] According to a fourth aspect of the present invention, in a method of forming an elastic bush having a cylindrical inner sleeve, an elastic member fixed on an outside surface of the inner sleeve and a cylindrical outer sleeve fixed on an outside surface of the elastic member, after fixing the inner sleeve, the elastic member and the outer sleeve, in order to subject the elastic member to compressive deformation, the diameter of the inner sleeve is increased or the diameter of the outer sleeve is decreased.

[0027] Thereby, since the elastic member is compressed beforehand, the fixing strength between the elastic member and both the sleeves is improved and also durability of the elastic member at the time of relative displacement of the inner sleeve and the outer sleeve in the rotational or axial direction is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a side view of a Cardan joint according to a first embodiment;

[0029]FIG. 2 is a vertical cross-sectional view of the yoke assembly according to a first embodiment;

[0030]FIG. 3 is an elevation view seen along the arrow A in FIG. 2;

[0031]FIG. 4 is an exploded vertical cross-sectional view of a yoke assembly according to a second embodiment;

[0032]FIG. 5 is an exploded vertical cross-sectional view of a yoke assembly according to a third embodiment;

[0033]FIG. 6 is an exploded vertical cross-sectional view of a yoke assembly according to a fourth embodiment;

[0034]FIG. 7 is an explanatory view showing the operation of the fourth embodiment;

[0035]FIG. 8 is a vertical cross-sectional view according to a fifth embodiment;

[0036]FIG. 9 is an elevation view seen along the arrow B in FIG. 8;

[0037]FIG. 10 is an elevation view of the elastic bush according to the fifth embodiment;

[0038]FIG. 11 is a cross-sectional view of the outer sleeve seen along the arrow C;

[0039]FIG. 12 is a cross-sectional view taken along line D-D in FIG. 10;

[0040]FIG. 13 is a vertical cross-sectional view of an elastic bush of a modification of the fifth embodiment;

[0041]FIG. 14 is a vertical cross-sectional view of a yoke assembly according to a sixth embodiment;

[0042]FIG. 15 is a vertical cross-sectional view showing a modification of the sixth embodiment;

[0043]FIG. 16 is a vertical cross-sectional view of a yoke assembly according to a seventh embodiment;

[0044]FIG. 17 is a vertical cross-sectional view of the elastic bush in FIG. 16;

[0045]FIG. 18 is a vertical cross-sectional view of a yoke assembly according to an eighth embodiment;

[0046]FIG. 19 is a vertical cross-sectional view showing a modification of the eighth embodiment;

[0047]FIG. 20 is an elevation view of an elastic bush according to a ninth embodiment;

[0048]FIG. 21 is an elevation view of an elastic bush according to a tenth embodiment;

[0049]FIG. 22 is an elevation view of an elastic bush according to an 11th embodiment;

[0050]FIG. 23 is an elevation view of an elastic bush according to a 12th embodiment;

[0051]FIG. 24 is a vertical cross-sectional view of a yoke assembly according to a 13th embodiment;

[0052]FIG. 25 is a vertical cross-sectional view of a yoke assembly according to a 14th embodiment;

[0053]FIG. 26 is an elevation view of the elastic bush of the 14th embodiment;

[0054]FIG. 27 is a horizontal cross-sectional view of an elastic bush according to a modification of the 14th embodiment;

[0055]FIG. 28 is a side view of an elastic bush according to a 15th embodiment;

[0056]FIG. 29 is a cross-sectional view taken along line E-E in FIG. 27;

[0057]FIG. 30 is a cross-sectional view taken along line F-F in FIG. 27;

[0058]FIG. 31 is a vertical cross-sectional view of a yoke assembly according to a 16th embodiment;

[0059]FIG. 32 is a vertical cross-sectional view of a yoke assembly according to a 17th embodiment;

[0060]FIGS. 33A an 33B are, respectively, a vertical cross-sectional view and an elevation view of a housing according to an 18th embodiment;

[0061]FIGS. 34A an 34B are, respectively, a vertical cross-sectional view and an elevation view of a housing according to a 19th embodiment;

[0062]FIGS. 35A an 35B are, respectively, a vertical cross-sectional view and an elevation view of a housing according to a 20th embodiment;

[0063]FIG. 36 is a vertical cross-sectional view of a housing according to a 21st embodiment; and

[0064]FIG. 37 is a vertical cross-sectional view of a housing according to a 22nd embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] An elastic shaft joint according to the present invention will be described in accordance with several embodiments.

[0066]FIG. 1 is a side view of a Cardan joint incorporating an elastic shaft joint (yoke assembly) according to a first embodiment. FIG. 2 is a vertical cross-sectional view of the yoke assembly. FIG. 3 is a front elevation seen along the arrow A in FIG. 2. As shown in FIG. 1, the Cardan joint is constituted of a yoke assembly 1, a counterpart-yoke 3, a cross joint 5 and a bearing (needle roller bearing) 7, and connects a first steering shaft 8 and a second steering shaft 9 rockably. The second steering shaft 9 is fitted in the yoke 3 and fixed thereto with a bolt or the like. It is to be noted that in the description of FIG. 2, the left side of the drawing is made to be a tip side or a forward side.

[0067] The yoke assembly 1 has a yoke 11 of a forging made of carbon steel, etc. (or a drawn product made of hot-rolled sheet steel), a shaft 13 of a press-formed product, etc. made of low carbon steel pipe, etc. and an elastic bush 15 for transmitting elastic torque between the yoke 11 and the shaft 13. The elastic bush 15 has a cylindrical inner sleeve fitted and fixed on the back end side of the yoke 11 by means of press fit, a cylindrical elastic member 19 fixed integrally to the outside surface of the inner sleeve 17 by means of vulcanized joining with synthetic rubber as its material, and a housing 21 with an approximately U-shaped vertical cross section fixed integrally to the outside surface of the elastic member 19 by means of vulcanizing joining. The first steering shaft 8 is fitted in and engaged with the shaft 13 via serrations, etc. so as to be movable in the axial direction. As a result, the shaft 13 is rotated in accordance with rotation of the first steering shaft 8 and absorbs movement in the axial direction occurring due to the rotation.

[0068] The housing 21 is constituted of a cylindrical outer sleeve 23 having the elastic member 19 fitted therein, a cylindrical elastic torque transmitting ring 25 fitted and fixed on the tip side of the shaft 13 by means of press fit, and a disc-like web 27 connecting the outer sleeve 23 and the elastic torque transmitting ring 25. The reference number 29 in FIG. 2 indicates a hole formed in the web 27. When performing press fit of the inner sleeve 17 to the yoke 11, a pressing jig is inserted through the hole 29. Besides, when performing press fit of the inner sleeve 17 to the yoke 11, the web 27 may be directly pressed, taking advantage of elastically deformable characteristics of the elastic bush 15 in the axial direction. The reference number 31 in FIGS. 2 and 3 indicates a stopper protrusion, and the reference number 33 indicates a recess, which is formed in the yoke 11 and in which the stopper protrusion is loose-fitted.

[0069] In the first embodiment, as the above structure is taken, the diameter of the elastic member 19 is made substantially larger as compared to conventional devices. As a result, while sufficient torsional rigidity between the yoke 11 and the shaft 13 is maintained, it is possible to effectively prevent inclination of the yoke assembly 1 causing deterioration of response of the steering system. In addition, since components of the conventional device disclosed in the Japanese Patent Application Laid-Open No. 8-170647 can be utilized for the yoke 11 and the shaft 13, reduction of the component management and manufacturing cost can be realized. The transmission of large torque is carried out by the contact of the stopper protrusion 31 of the shaft 13 onto the inside surface of the recess 33 of the yoke 11.

[0070]FIG. 4 is an exploded vertical cross-sectional view of a yoke assembly according to a second embodiment. The completed form and operation of the yoke assembly of the second embodiment are identical to those of the first embodiment, but the structure of the elastic bush 15 is different. That is, in the elastic bush 15 of this embodiment, the elastic member 19 is attached to the inner sleeve 17 by means of vulcanized joining, constituting one component separately from the housing 21. Therefore, in forming the yoke assembly 1, after the inner sleeve 17 is forced onto the yoke 11, the outer sleeve 23 of the housing 21 is forced and fixed to the elastic member 19, or after the elastic member 19 is forced and fixed to the outer sleeve 23, the inner sleeve 17 is forced upon the yoke 11. Besides, the elastic member 19 and the outer sleeve 23 may be fixed each other via adhesive instead of press fit or may be fixed via both press fit and adhesive.

[0071]FIG. 5 is an exploded vertical cross-sectional view of a yoke assembly according to a third embodiment. The completed form and operation of the yoke assembly 1 of the third embodiment is approximately identical to those of the first embodiment, but the structure of the elastic bush 15 is different. That is, in the elastic bush 15 of this embodiment, the elastic member 19 and the outer sleeve 23 of the housing 21 are fixed each other by means of vulcanized joining, and the inner sleeve is omitted differently from the above embodiments. The elastic member 19 is forced directly upon the yoke 11. The elastic member 19 and the yoke 11 may be fixed each other via adhesive instead of press fit, or may be fixed via both press fit and adhesive.

[0072]FIG. 6 is an exploded vertical cross-sectional view of a yoke assembly according to a fourth embodiment. The completed form and operation of the yoke assembly 1 of the fourth embodiment is approximately identical to those of the third embodiment, but the structure of the elastic member 15 is different. That is, the elastic bush 15 of this embodiment is the elastic member 19 itself, and the elastic member 19 is directly forced upon the yoke 11 and the outer sleeve 23 of the housing 21. Besides, the fixing of the elastic member 19 to the yoke 11 and the outer sleeve 23 may be performed via adhesive instead of press fit, or may be performed via both press fit and adhesive.

[0073] In the case of depending on only press fit fixing, when the yoke 11 and the shaft 13 are relatively shifted in the axial direction, the elastic member 19 might be slipped against the yoke 11 and the housing 21. In this case, as shown in the assembled state of FIG. 7, when the shaft 13 is moved by the distance t1 backward with respect to the yoke 11, the stopper protrusion 31 is brought into contact with the end surface of the recess 33 to be stopped, or when the housing 21 is moved forward by the distance t2 with respect to the yoke 11, the web 27 is brought into contact with the back end of the yoke 11 to be stopped, thereby preventing excessive slip of the elastic member 19. This operation is the same in the first and third embodiments when the elastic member 19 is forced upon the housing 21 and the yoke 11.

[0074]FIG. 8 is a vertical cross-sectional view of a yoke assembly according to a fifth embodiment. FIG. 9 11 is a front elevation seen along the arrow B in FIG. 8. FIG. 10 is a front elevation of the elastic bush. FIG. 11 is a cross-sectional view of the outer sleeve seen along the arrow C in FIG. 10. FIG. 12 is a cross-sectional view taken along line D-D. As shown in FIG. 8, in the yoke assembly of this embodiment, differently from the above embodiments, the elastic bush 15 is connected to the shaft 13 via a separate elastic torque transmitting member 41.

[0075] The elastic torque transmitting member 41 is approximately U-shaped in the vertical cross section similarly to the outer sleeves 23 of the first to fifth embodiments. An outer ring 43 is fitted and fixed onto the outer sleeve 23 of the elastic bush 15, and an inner ring 45 is fitted and fixed onto the tip side of the shaft 13. Also, in the elastic bush 15 of this embodiment, as shown in FIGS. 10 to 12, the elastic member 19 is mounted between the cylindrical inner and outer sleeves 17 and 23. Te elastic member 19 is formed cylindrically and integrally, but is zigzag-shaped to have large areas on both end portions in the axial direction.

[0076] In the fifth embodiment, since the above structure is taken, the diameter of the elastic member 19 is increased similarly to the first embodiment, and the elastic member 19 is lopsidedly distributed so as to be large on the both end portions in the axial direction. As a result, while sufficient torsional rigidity between the yoke 11 and the shaft 13 is maintained, it is possible to effectively prevent inclination of the yoke assembly 1 causing deterioration of response in the steering system, and to reduce rigidity of the yoke assembly 1 in the axial direction causing vibration and noise.

[0077]FIG. 13 shows a modification of the fifth embodiment, corresponding to FIG. 12. In the modification, after the elastic member 19 is fixed to the inner sleeve 17 and the outer sleeve 23 by means of vulcanized joining, the diameter of the inner sleeve 17 is increased or the diameter of the outer sleeve 23 is decreased. As shown in the drawing, the compressed elastic member 19 is swelled out between the inner sleeve 17 and the outer sleeve 23. In this modification, thus the elastic member 19 is compressed beforehand, so that wave-like flex deformation occurs in polymers forming the elastic member 19. Thereby, when the inner sleeve 17 and the outer sleeve 23 are relatively displaced in the rotational direction or axial direction, the deformed polymers are extended to be almost the original form. Consequently, scission of the polymers causing fatigue failure of the elastic member 19 becomes hard to happen, leading to enhancement of durability of the elastic member 19 (i.e. the elastic bush 15).

[0078]FIG. 14 is a vertical cross-sectional view of a yoke assembly according to a sixth embodiment. In the yoke assembly of this embodiment, the elastic torque transmitting member 41 the same as in the fifth embodiment is utilized, but a pair of elastic bushes 15 are disposed before and after a spacer 51.

[0079] In the sixth embodiment, since thus structure is taken, the diameter of the elastic members 19 is increased similarly to the first embodiment, and the elastic members 19 are lopsidedly disposed on both end sides in the axial direction. As a result, similarly to the fifth embodiment, while sufficient torsional rigidity between the yoke 11 and the shaft 13 is maintained, it is possible to effectively prevent the inclination of the yoke assembly 1 causing deterioration of response of the steering system, and to reduce rigidity of the yoke assembly 1 in the axial direction causing vibration and noise.

[0080]FIG. 15 is a vertical cross-sectional view showing a modification of the sixth embodiment. In this embodiment, similarly to the modification of the fifth embodiment, after the elastic member 19 is fixed to the inner sleeve 17 and the outer sleeve 23 by means of vulcanized joining, the diameter of the inner sleeve 17 is increased, or the diameter of the outer sleeve 23 is reduced, and the operation and effect are the same as those in the modification of the fifth embodiment.

[0081]FIG. 16 is a vertical cross-sectional view of a yoke assembly according the seventh embodiment. FIG. 17 is a vertical cross-sectional view of the elastic bush. In the yoke assembly of this embodiment, similarly to the sixth embodiment, a pair of elastic bushes 15 are used, but the elastic bushes 15 are in contact with each other without using a spacer. That is, in this embodiment, the elastic member 19 is disposed lopsidedly on the one end side of the elastic bush 15, and the identical elastic bushes 15 are forced upon so as to face each other between the yoke 11 and the outer ring 43 of the elastic torque transmitting member 41 such that the elastic members 19 are disposed respectively on both end sides in the axial direction. Further, the rear elastic bush 15 is projected beyond the rear end of the yoke 11. Also, the elastic bushes 15 are compressed beforehand similarly to the modification of the fifth embodiment.

[0082] The operation and effect of the seventh embodiment are approximately identical to those of the modification of the fifth embodiment, but the number of components and the number of manufacturing processes are reduced, so that the manufacturing cost is lowered. Also, since the distance between the elastic members 19 is taken adequately, the inclination of the yoke 11 and the shaft 13 is effectively prevented. In addition, the elastic bush 15 is projected beyond the end of the yoke 11, so that the entire length of the yoke 11 can be shortened to reduce its weight.

[0083]FIG. 18 is a vertical cross-sectional view of a yoke assembly according to an eighth embodiment. FIG. 19 is a vertical cross-sectional view of a modification of the eighth embodiment. The yoke assembly of the eighth embodiment has a structure approximately identical to that of the fifth embodiment, but 3-set six elastic bushes 53, 55 and 57 with different rigidity are provided. Before and after the spacer 51, the elastic bushes 53 with high rigidity are disposed on both end portions and the elastic bushes 57 with low rigidity are disposed on central portions.

[0084] As thus structure is taken in the eighth embodiment, it is possible to prevent inclination of the yoke assembly 1 and to reduce rigidity thereof in the axial direction further as compared with the fifth embodiment. In the modification shown in FIG. 19, the elastic members of the elastic bushes 53, 55 and 57 are compressed in advance, whose operation and effect are the same as those of the modification of the fifth embodiment.

[0085] FIGS. 20 to 23 are elevation views of elastic bushes according to ninth to twelfth embodiments. In these embodiments, cross sections of all the elastic bushes 15 are noncircular shape. In the ninth to eleventh embodiments, the inner sleeve 17 and the outer sleeve 23 are oval shape, and the elastic members 19 are properly disposed. That is, in the ninth embodiment, the elastic member 19 is disposed between the inner sleeve 17 and outer sleeve 23 without space. In the tenth embodiment, the elastic members 19 are disposed only between linear portions of the inner sleeve 17 and the outer sleeve 23. In the eleventh embodiment, six elastic members 19 are disposed at proper intervals between the inner sleeve 17 and the outer sleeve 23. On the other hand, in the twelfth embodiment, the inner sleeve 17 and the outer sleeve 23 are in the shape of a polygonal (triangle), and three elastic members 19 are disposed between those excluding corner portions.

[0086] Thus, the shapes of the cross sections of the elastic bushes 15 in the ninth to twelfth embodiments are made noncircular, so that at the time of relative rotation of the inner sleeve 17 and the outer sleeve 23, a portion or most portions of the elastic members 19 are compressed and deformed. Thereby, it is possible to obtain the yoke assembly whose torsional rigidity is improved without increasing rigidity in the axial direction.

[0087]FIG. 24 is a vertical cross-sectional view of a yoke assembly according to a thirteenth embodiment. In the thirteenth embodiment, the yoke assembly is constituted of the yoke 11, the solid shaft 13 and a large torque transmitting pin 61, but the structure of the elastic bush 15 is approximately identical to that of the fifth embodiment and so the operation and effect are the same also.

[0088]FIG. 25 is a vertical cross-sectional view of a yoke assembly according to a fourteenth embodiment. FIG. 26 is an elevation view of the elastic bush thereof. FIG. 27 is a horizontal cross-sectional view showing an essential part of the elastic bush thereof. Although the structure of the fourteenth embodiment is approximately the same as that of the aforementioned fifth embodiment, the shape of the elastic torque transmitting member 41 and the structure and shape of the elastic bush 15 are different. That is, in this embodiment, the outer ring 43 of the elastic torque transmitting member 41 has a plurality of irregularities and a wave-shaped cross section, and the outer surface of the elastic member 19 of the elastic bush 15 has a corresponding shape to the outer ring 43. A portion of the inner sleeve 17 in the axial direction is formed to be a complete round as shown in FIG. 26, and the remnant portion thereof is formed to have a wave-shaped cross section as shown in FIG. 27. In addition, the elastic bush 15 does not have an outer sleeve, and the elastic member 19 is forced lightly upon the outer ring 43 of the elastic torque transmitting member 41. Also, the outer ring 43 of the elastic torque transmitting member 41 and the elastic member 19 are provided on center portions in the axial direction with steps to facilitate press fit.

[0089] In the fourteenth embodiment, thus, the horizontal cross sections of the outer ring 43 of the elastic torque transmitting member 41 as well as the elastic member 19 is made in the shape of wave, so at the time of relative rotation of the inner sleeve 17 and the outer sleeve 23, a portion of the elastic member 19 is compressed and deformed. Thereby, it is possible to obtain the yoke assembly capable of realizing both maintenance of the torsional rigidity and convenience of assembly without increasing rigidity in the axial direction.

[0090]FIG. 27 is a cross-sectional view of an elastic bush according to a modification of the fourteenth embodiment. In this modification, the cross section of the inner sleeve 17 is wave-shaped over the entire area in the axial direction correspondingly to the outer sleeve 23, contributing to further enhancement of torsional rigidity as compared with the fourteenth embodiment.

[0091]FIG. 28 is a side view of the elastic bush 15 according to a fifteenth embodiment. FIG. 29 is a cross-sectional view taken along line E-E line in FIG. 28. FIG. 30 is a cross-sectional view taken along line F-F line in FIG. 28. As shown in FIGS. 28 to 30, in the elastic bush 15 of the fifteenth embodiment, the outer sleeve 23 is provided on the center portions in the axial direction at intervals of a predetermined angle with rectangular holes 71, while the elastic member 19 is provided in positions corresponding to the holes 71 with recesses 73.

[0092] Owing to this structure of the fifteenth embodiment, at the time of vulcanized joining, it is possible to easily form the elastic bush 15 with the elastic member 19 lopsidedly distributed so as to have large areas on both the end portions in the axial direction, and to obtain the identical operation and effect to those of the fifth embodiment.

[0093]FIG. 31 is a vertical cross-sectional view of a yoke assembly according to a sixteenth embodiment. Although the structure of the sixteenth embodiment is approximately the same as that of the first embodiment, a slipping-off preventing ring 81 is attached to the rear end surface of the housing 21. The slipping-off preventing ring 81 is a disc spring or the like, and is disposed with respect to the shaft 13 in a direction for inhibiting advance thereof. Therefore, at the time of a collision of an automobile, even though a driver bumps against a steering wheel to cause the first steering shaft 8 to enter into the shaft 13, and the shaft 13 is dragged by the first steering shaft 8 to advance, the slipping-off preventing ring 81 bites into the surface of the shaft 13 to inhibit advance of the shaft. As a result, separation of the yoke 11 and the shaft 13 is prevented and smooth collapse of the steering shaft is realized.

[0094]FIG. 32 is a vertical cross-sectional view of a yoke assembly according to a seventeenth embodiment. The structure of the seventeenth embodiment is also approximately the same as that of the first embodiment, but the vertical cross section of the housing 21 is almost L-shaped, and the elastic torque transmitting ring 25 is formed so as to extend backward, and fitted and forced upon the shaft 13. The shaft 13 is provided in the vicinity of the rear end portion of the elastic torque transmitting ring 25 with an annular groove 83. The rear end portion of the elastic torque transmitting ring 25 is crimped, and its crimped portion 85 is fitted in the annular groove 83. Thereby, also in this embodiment, relative movement of the elastic torque transmitting ring 25 and the shaft 13 is limited, so that the operation and effect the same as in the sixteenth embodiment is obtainable.

[0095]FIGS. 33A and 33B are, respectively, vertical cross-sectional view and an elevation view of the housing 21 according to an eighteenth embodiment. Although the structure of the eighteenth embodiment is almost the same as that of the first embodiment, a plurality of ribs 93 a are provided on an inner cylinder looped portion 91 of the disc-like web 27 connecting the outer sleeve 23 of the housing 21 and the elastic torque transmitting ring 25. Consequently, the rigidity of the disc-like web 27 can be secured to make it hard to be deformed, leading to enhancement of the strength of the housing 21. The volume and number of the ribs 93 a may be adjusted properly in accordance with a desired strength. Also, in this embodiment, the same operation and effect as in the first embodiment can be obtained.

[0096]FIGS. 34A and 34B are, respectively, a vertical cross-sectional view and an elevation view of the housing 21 according to a nineteenth embodiment. Although the structure of the nineteenth embodiment is almost the same as that in the first embodiment, a plurality of beads 95 are provided on the disc portion of the disc-like web 27 connecting the outer sleeve 23 of the housing 21 and the elastic torque transmitting ring 25 so as to extend radially from the center of the housing 21. As a result, the rigidity of the disc-like web 27 can be secured to make it hard to be deformed, contributing to enhancement of the strength of the housing 21. Besides, the same operation and effect as in the first embodiment can be obtained.

[0097] The shapes (width, depth, shape of the cross section, etc.) of the beads 95 and a combination of the shapes may be selected properly in compliance with a desired design strength.

[0098]FIGS. 35A and 35B are, respectively, a vertical cross-sectional view and an elevation view of the housing 21 according to a twentieth embodiment. Although the structure of the twentieth embodiment is almost the same as that in the first embodiment, a plurality of dimples are provided on the disc portion of the disc-like web 27 connecting the outer sleeve 23 of the housing 21 and the elastic torque transmitting ring 25. As a result, the rigidity of the disc-like web 27 can be secured to make it hard to be deformed, contributing to enhancement of the strength of the housing 21. Also, in this embodiment, the same operation and effect as in the first embodiment can be obtained. The shapes (diameter, depth, etc.) of the dimples 96, a combination of the shapes and the density of the dimples 96 may be selected in compliance with a desired design strength.

[0099]FIG. 36 is a vertical cross-sectional view of the housing 21 according to a twenty-first embodiment. Although the structure of the twenty-first embodiment is almost the same as that in the first embodiment also, the disc portion of the disc-like web 27 connecting the outer sleeve 23 of the housing 21 and the elastic torque transmitting ring 25 is formed such that the bend raising or bend radius R of the inner cylinder looped portion 91 of the housing 21 and the bend raising or bend radius R of an outer cylinder looped portion 92 are continuous (i.e., The disc portion is formed semicircular). As a result, the rigidity of the disc-like web 27 can be secured to make it hard to be deformed, contributing to enhancement of the strength of the housing 21. Also in this embodiment, the same operation and effect as in the first embodiment can be obtained.

[0100]FIG. 37 is a vertical cross-sectional view of the housing 21 according to a twenty-second embodiment. Although the structure of the twenty-second embodiment is almost the same as that of the first embodiment, the disc portion of the disc-like web 27 connecting the outer sleeve 23 of the housing 21 and the elastic torque transmitting ring 25 is formed such that the bend raising or the bend radius R1 of the inner cylinder looped portion 91 of the housing 21 is defined with respect to the bend raising or the bend radius R2 of the outer cylinder looped portion 92 so as to be R2<R1. As a result, the rigidity of the disc-like web 27 can be secured to make it hard to be deformed, contributing to enhancement of the strength of the housing 21. Also in this embodiment, the same operation and effect as in the first embodiment can be obtained.

[0101] The description of the embodiments according to the present invention is completed now, but the present invention is not limited thereto. For example, although the present invention is applied to the Cardan joint in the above embodiments, but may be applied to a double Cardan joint and a Birfield joint. Further, the structure and shape of the elastic bush, the material and detailed shape of the elastic member may be altered properly without deviating the scope of the purpose of the present invention.

[0102] As mentioned above, according to the elastic shaft joint of the present invention, while sufficient torsional rigidity between the joint member and the shaft member is secured, inclination of the elastic shaft joint causing deterioration of response of the steering system can be effectively prevented, and rigidity of the elastic shaft joint in the axial direction causing vibration and noise can be reduced. 

What is claimed is:
 1. An elastic shaft joint comprising: a joint member; a shaft member being fitted in a shaft of said joint member; and an elastic bush having a cylindrical inner sleeve fitted and fixed on said joint member, a cylindrical elastic member fixed on an outside surface of said inner sleeve, and a cylindrical outer sleeve fixed on an outside surface of said elastic member, for elastic torque transmission between said joint member and said shaft member, wherein said outer sleeve is fixed on said shaft member.
 2. An elastic shaft member comprising: a joint member; a shaft member being fitted in a shaft of said joint member; an elastic bush having a cylindrical inner sleeve fitted and fixed on said joint member, an elastic member fixed on an outside surface of said inner sleeve, and a cylindrical outer sleeve fixed on an outside surface of said elastic member, for elastic torque transmission between said joint member and said shaft member; and a torque transmitting member whose one end is fitted and fixed on said elastic bush and whose other end is fixed on said shaft member, wherein said elastic member is lopsidedly distributed largely on both end sides in the axial direction between said inner sleeve and said outer sleeve.
 3. An elastic shaft joint comprising: a joint member; a shaft member being fitted in a shaft of said joint member; a plurality of elastic bushes each having a cylindrical inner sleeve fitted and fixed on said joint member, an elastic member fixed on an outside surface of said inner sleeve, and a cylindrical outer sleeve fixed on an outside surface of said elastic member, for elastic torque transmission between said joint member and said shaft member; and a torque transmitting member whose one end is fitted and fixed on said plurality of elastic bushes and whose other end is fixed on said shaft member, wherein said plurality of elastic bushes are disposed between said joint member and said torque transmitting member on both end sides in the axial direction.
 4. An elastic shaft joint according to claim 3, wherein said plurality of elastic bushes constitute plural sets each which has said elastic member with different rigidity, and said elastic members with high rigidity are disposed on both end sides in the axial direction between said joint member and said torque transmitting member.
 5. An elastic shaft joint according to claim 1, wherein in said elastic bush, after said inner sleeve, said elastic member and said outer sleeve are fixed, in order to subject said elastic member to compressive deformation, the diameter of said inner sleeve is increased or the diameter of said outer sleeve is decreased.
 6. An elastic shaft joint according to claim 2, 3 or 4, wherein in said each elastic bush, after said inner sleeve, said elastic member and said outer sleeve are fixed, in order to subject said elastic member to compressive deformation, the diameter of said inner sleeve is increased or the diameter of said outer sleeve is decreased.
 7. An elastic shaft joint according to claim 2, 3 or 4 wherein a cross section of said each elastic bush taken perpendicular to the axis of said elastic bush is formed noncircular so as to subject said elastic member to compressive deformation at the time of relative rotation of said inner sleeve and said outer sleeve.
 8. A method of forming an elastic bush having a cylindrical inner sleeve, an elastic member fixed on an outside surface of said inner sleeve and a cylindrical outer sleeve fixed on an outside surface of said elastic member, comprising: increasing the diameter of said inner sleeve or decreasing the diameter of said outer sleeve so as to subject said elastic member to compressive deformation after fixing said inner sleeve, said elastic member and said outer sleeve. 